What keeps wheels down in hard turns?

[Boxer12]

Is wheel lift a function of the spring weight or the swaybar? Does this look like I need a stiffer swaybar or springs?

 

[ViperGeorge]

Did you go over the curbing at the apex? If so it looks like it loaded the outside wheel and lifted the inside wheel. I think this is the result of a stiff suspension but then I don't know squat about springs and shocks.

 

[2000_Black_RT10]

Rebound adjustment on the damper can also contribute at higher speed, too much damping on rebound and not enough time for the wheel to drop. Try jacking the car up on the passenger side and compare pics. If it's much more droop when stationary, I'd lean towards the rebound adjustment. If not.. then, yes sway bar can keep the tire up, but then may also need to look at compression settings on damper to level out some of the body roll and spring rates.

Regards,
Mike

 

[Paul Hawker]

Also don't know what causes this, but that is a really cool picture.

Especially like the way your eyes are already looking ahead to the next corner.

 

[VIPER GTSR 91]

Archer Racing would be a good place to start with this question and they are excellent at set ups for your car, but without knowing the specific forces in the turn i.e. speed on entry or track out, degree of turn, etc. I would think it would be hard to diagnose with just this picture and no data. Give them a call.

 

[Red Snake]

You just need to SLOW down, lol. You are going too fast.

 

[GTS Dean]

Answer to the original question: Gravity.

To me, it doesn't look like the tire is off the ground. The daylight is due to camber - not enough body roll for it to lift mechanically, so I'd suspect possibly too much rebound on the RF shock. Were you on the throttle at this point? If so, you'd have rear weight transfer unloading the opposite corner - in this case, the RF. Something else you could try is more bump at the Left Rear to slow the weight transfer, but this is just one tiny slice of one corner out of the entire lap.

 

[Boxer12]

To give more details, I was accelerating through the flat esses (this was taken just past the exit of 6a). Yes, I did just travel over the curb. Rebound was set at 8 on the rt fr. Shock at 10.

Idk if it was off the ground, but the fr of the car would slide a bit coming off that corner (minimal contact) and I would have to catch it while I was rolling on the accelerator hard. It has done this before on corner exit.

PS-Archer did my track alignment but I have not had it corner balanced.

 

[GTS Dean]

To give more details, I was accelerating through the flat esses (this was taken just past the exit of 6a). Yes, I did just travel over the curb. Rebound was set at 8 on the rt fr. Shock at 10.

Idk if it was off the ground, but the fr of the car would slide a bit coming off that corner (minimal contact) and I would have to catch it while I was rolling on the accelerator hard. It has done this before on corner exit.

PS-Archer did my track alignment but I have not had it corner balanced.

I'm not familiar with the ACR shocks. 8 and 10 out of what? If memory serves, my Penskes have like 32 sweeps of rebound, 16 clicks of LSB and 12 clicks of HSB.

I own scales and personally think that for even a moderate trackrat, corner weighting is oversold. Sure, you don't want to be wildly off, but as soon as you put the car under dynamic loads, it comes down to time in the corner and overall balance.

 

[mjorgensen Woodhouse]

If you have any kind of data logging it would show if the car suddenly lost traction because of flying a tire. This is not always a big deal as long as the balance feels right. I to agree that the wheel is on the ground and it is an illusion. The Negative camber on that light tire is what makes this appear to be lightened more than it is.

 

[Boxer12]

Here is what the data logger recorded...just GPS data (no sensors on wheels, etc)

 

[GTS Dean]

To give more details, I was accelerating through the flat esses (this was taken just past the exit of 6a). Yes, I did just travel over the curb.

Idk if it was off the ground, but the fr of the car would slide a bit coming off that corner (minimal contact) and I would have to catch it while I was rolling on the accelerator hard. It has done this before on corner exit.

Sounds like you're going to have to experiment more with shock settings or your line if you continue to tag that apex curb - since it unloads and unsettles the front. Since it's a slow-medium speed corner, you should work on mechanical grip. Too much shock stiffness will make it harder to put power down. You may need to apex a little later, or drive a cleaner line without using the curb. A later apex means a wider entry, which may leave the door open for someone to stick their nose down the inside.

 

[Viper X]

Couple of thoughts,

I have the same color ACR so it's cool to see this pic.

1 - The OE front springs in the ACR are very light at just over 500 inch / lbs, so the car will roll a bunch up front. Heavier front springs have worked very well for me. As an aside, I'd be interested to know the spring rates of the new ACR X if anybody knows. Likely, they will be close to the comp coupe at 1100 front, 1500 rear.

2 - Don't know if you have the adjustable sway bar end links but if not, get them. The sway bars in the ACR are from the comp coupe, so they are plenty stout.

3 - Not sure what tires you are running but some tires like more negative camber than others.

Dan

 

[Boxer12]

Thanks for the input Dan! I agree, the color combo is the best!! I was running A6's when this pic was shot. I was already planning to get the adjustable sway bar links. I was also thinking along the lines of heavier springs but my concern is in regard to tracks like Miller or VIR where you hit the curbing pretty hard and how it might unsettle the car. Where do you run? Do they have gators? Maybe I should get a second set of shocks/springs and try swapping them out. Wouldn't I have to change the alignment too (whenever I changed the shock/spring out)?

Here is a pic of the fr springs in the ACR-X test mule...not sure if the production ACR-X will have the same springs (I was looking at the production pics on VRH site, and they don't look as stout to me).

 

[Viper X]

Hey Boxer12,

I know there are curbs (gators?) on some tracks that you need to drive over to obtain your best laps times, but generally, I try to avoid "hitting" them if they are steep and upset the car.

As for stiffer springs, my ACR has reacted very well to them. You will likely want to stiffen up the shocks a bit if you stiffen the springs. I went to Moton Motorsports shocks and prefer them to the OE set up.

As for changing your alignment when changing springs, just maintain the same ride height and you'll be OK.

As for tracks, the local road courses that I run are Buttonwillow, Willow Springs, Auto Club Speedway and Spring Mountain.

I am looking forward to driving Miller with Viper Days this fall at VOI 11 - I've not made it there yet. I would like to know which configuration NARRA is planning to run at Miller. Perhaps I'll see you there.

Dan

 

[Boxer12]

Dan, I think I will try to pick up a spare set of KW's and put heavier springs on them to run smooth tracks that don't have gators. Maybe I will upgrade to Motons when I wear out the KWs.

If you go to Miller, you will definately have to pound some high curbs to get the best lap times. At Sebring, where I saw the ACR-X and took the pic above, you really don't have anything too drastic to upset the car and although it is known as a rough track, it is not like running full tilt over curbs (ala VIR where you are going about 130-140 on the uphill esses) and gators (ala Road America). If you haven't met 'gators' yet, you are in for an interesting challenge. Most places where they exist, guys run right over top of them (me included), and it will rattle your teeth out if you are set up too stiff.

I plan to be at VOI11. Its a great track, and I think you will find it worth the haul. See you there.

 

[j-rho]

Saturation of available weight transfer on the axle is what generally causes wheel lift when not talking about curbs/jumps. Lowering the CG height is the only good way to reduce overall weight transfer, and keep more weight on the inside tire.

I run my 2004 on stock springs and ride height, which causes really light inside tires at times. As Mark W said, as long as it does it in a smooth and predictable way, you won't necessarily notice it when driving.

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[Viper X]

Hey Boxer 12,

Spring changes are pretty easy with the ACR's KW shocks. You could pick up a few sets of heavier springs and try them fairly easily - you don't really need spare shocks.....

Dan

 

[Boxer12]

Hey Boxer 12,

Spring changes are pretty easy with the ACR's KW shocks. You could pick up a few sets of heavier springs and try them fairly easily - you don't really need spare shocks.....

Dan

Good to know. I am going to try that. Don't you have to do a complete realignment when you change springs?

J-Rho, The car is lowered as far as I can without going to 18" rear wheels. I feel push when the car is on one front tire.

Here (#302) is another example...this past weekend at Mid-O.
HPDE 4 & Time Trials - FTWMotorsports' Photos

 

[Viper X]

Hey Boxer 12,

I ran Buttonwillow last weekend with my ACR running 1100 / 1500 springs as a "test and tune". I'm still enjoying playing with shocks, springs, etc.

To get the fastest lap times at BW, there are at least 4 "berms" that you must drive over. I found that if I preloaded the suspension (with weight transfer) before driving over these berms, the wheel on the berm went over it much more easily and I did not upset the suspension (balance of the car) nearly as much.

Another thing that may help is installing polyurethane sway bar bushings, if you haven't already.

On the "front tire pushing", many of us out West have gone to 305 or even 315 front tires on 11 inch rims with 2.5 - ish negative front camber. This helps balance the car on some tracks, i.e. much less "pushing".

Most of our tracks out west are anything but smooth.

Look forward to Miller.

Dan

 

[GTS Dean]

On the "front tire pushing", many of us out West have gone to 305 or even 315 front tires on 11 inch rims with 2.5 - ish negative front camber. This helps balance the car on some tracks, i.e. much less "pushing".

some of us in Texas have been doing 315's on 10" rims since about '94 on our Gen 1s.

 

[Viper X]

some of us in Texas have been doing 315's on 10" rims since about '94 on our Gen 1s.

This depends on the specific tire; some are wider than others and what you would consider "acceptable" tire wear and performance.

I and others in our club have tried running Hoosier R6's in 315 x 30 x 18 up front on 10 inch rims on our SRTs / ACRs. We found that the front tires overheated and wore out prematurely. The car also continued to "push" more than when running the proper rim size.

Dan

 

[j-rho]

Tires work best when supported by proper width wheels, and 315 Hoosiers prefer something 11-12" wide. But even when limited to 10", the 315 will provide more grip than the 275 or 295, something like
(275 on 10") < (315 on 10") < (315 on 12")

Believe it or not, I actually found front grip improvements going from a 315 to a 335 front tire, while still on the rules-mandated 10" front wheels. The extra weight and drag might not be worth it on the track but works great for autocross.

 

[Boxer12]

I have run 315's as well, with an aggressive track alignment. It isn't as nimble (eg., uphill esses at VIR), but has less push in the higher speed corners. I found that too much wing also creates push in the high speed corners. Poly bushings are sitting in toolbox...need to get them on. Maybe this weekend.